This invention is directed generally to hydraulic cylinders, and specifically to a hydraulic cylinder with an improved cushion device thereon.
Modern industry has found many important functions for hydraulic cylinders which were heretofore met by more complex and costly mechanical mechanisms. The invention herein described and claimed relates primarily to hydraulic cylinders which must change speed at the end of a stroke to absorb the shock produced by a high mass workload and/or high piston speed.
The concept of a cushion pin is not per se new. An example can be found in the bale wagon art, where, some time ago it was observed that the cylinder which rapidly raises and lowers the heavy second table (see U.S. Pat. No. 4,088,231) encountered severe undesirable shock loads, particularly at the end of the retraction phase of the cycle. The solution to this problem was envisioned to be the employment of a rigid pin on the face of the cylinder piston which moved into and out of a fluid flow port to restrict the flow of hydraulic fluid therethrough, and, thus, break or "cushion" the motion of the piston. The cushion pin used was rigidly affixed to the piston face and had to be carefully sized and oriented relative to the fluid flow port. While the fixed pin concept improved the cylinder operation, it was impossible to build such a mechanism with very small clearances between the pin and the walls of the fluid flow port. As one of skill in the art will readily appreciate, inherent machining tolerances permit a minimum clearance between concentric circular components of about 1/32 of an inch. Since much smaller clearances are often desirable, the prior art permitted only a limited selection of cylinder operating characteristics.